An antiglare optical film is generally disposed on the outermost surface of a display in a display device such as a plasma display (PDP), an electroluminescence display (ELD) or a liquid crystal display device (LCD) for preventing the formation of reflected images caused by reflection of external light.
With the recent rapid increase in the size of display screens as typically observed in liquid crystal TVs and so on, antiglare optical films are utilized not only in household devices but also in devices to be placed in larger rooms such as station or airport waiting rooms. Under these circumstances, it becomes necessary to prevent the formation of reflected images caused by reflection of external light under various indoor environments over a wide range.
To prevent the formation of reflected images caused by reflection of external light, it has been a common practice to employ an antiglare optical film having a concavo-convex shape on the surface (a tilted plane) whereby the outline of a reflected image is blurred. Thus, the visibility in the specular reflection direction of external light is improved. On the other hand, however, scattering lights enter directions other than the specular reflection direction and thus a black image takes on whitish looks (i.e., the phenomenon called “white blur”). Therefore, attempts have been made to exclusively elevate the effective antiglare components (tilted plane components) to thereby prevent both of the formation of reflected images and white blur (see, for example, WO 2006/088203, JP-A-2007-41533, JP-A-2005-195819 and JP-A-2007-187952), wherein the tilt angles of the peaks and valleys (concavity and convexity) on the surface are defined.
In the case where a display is placed in a larger room such as a station or airport waiting room, however, there are multiple lighting fixtures at short and long distances from the display. By using the existing techniques as discussed above, it is difficult to stably prevent both of the formation of reflected images and white blur caused by these lighting fixtures at short and long distances from the display. In the case of placing a large-sized display of 32 inches or more in a large room, the above-described phenomena become particularly serious and, therefore, it has been required to develop techniques for overcoming these problems.